An investigating officer in the case against a U.S. Marine accused of murdering civilians in Haditha, Iraq, has recommended that charges against him be dropped, concluding that the government's allegations that the Marine executed a group of men are "unsupported and incredible."

The findings by Marine Lt. Col. Paul Ware could exonerate Lance Cpl. Justin Sharratt, who formed part of a convoy that was struck by a roadside bomb in Haditha on Nov. 19, 2005. Members of his unit -- Kilo Company, 3rd Battalion, 1st Marine Regiment -- allegedly killed a group of young men who were ordered out of a nearby car. The Marines then went house to house, allegedly killing as many as two dozen people, including women and children.

Ware's 18-page report, released by Sharratt's attorneys, was submitted Friday to Lt. Gen. James Mattis, commander of the 1st Marine Expeditionary Force. Mattis could disregard the recommendation and order an administrative punishment or a court-martial, but it would be unusual for a commanding officer to go against such a strongly worded conclusion, legal experts said.

The report on Sharratt's case came on the same day that a separate investigation recommended a court-martial for Lt. Col. Jeffrey Chessani, a Marine battalion commander charged with dereliction of duty in not properly reporting the Haditha killings. In a report obtained by The Washington Post, the investigating officer, Col. Christopher Conlin, wrote that Chessani "failed to thoroughly and accurately report and investigate a combat engagement that clearly needed scrutiny." Conlin added that Chessani "suffered from a fatal misunderstanding that loyalty to his Marines meant vigorously defending their actions to the detriment of determining what those actions actually were."

Sharratt, 22, of Canonsburg, Pa., did not take part in the first shootings on Nov. 19, and he has acknowledged killing a group of men in a home later that day, when, he said, he believed they raised weapons at him. Sharratt told investigators that he used a 9mm pistol to shoot them as he and Staff Sgt. Frank Wuterich searched the home.

"He responded instinctively, assaulting into the room and emptying his pistol," Ware wrote. "Whether this was a brave act of combat against the enemy or tragedy of misperception born out of conducting combat with an enemy that hides among innocents, LCpl Sharratt's actions were in accord with the rules of engagement."

The rules of engagement have become central in the Haditha cases, as defense attorneys have argued that the troops used aggressive but approved tactics to assault what they thought were enemy targets. The first shootings have garnered more investigative attention because they came immediately after a Marine was killed in an explosion and because unarmed people were killed.

Sharratt's incident in 2005 came hours later, after Marines swarmed the scene to secure the area. Sharratt and others noticed suspicious behavior in the home before entering and shooting, they said. Marines reported finding two AK-47 rifles in the house.

Ware's recommendations came after Sharratt's military Article 32 hearing, the equivalent of a civilian grand jury proceeding. Ware, a military judge, weighed evidence from prosecutors and defense attorneys, and read thousands of pages of documents. He also suggested that Sharratt be given immunity to testify in other Haditha-related cases.

"This is just a big relief for us," said Sharratt's mother, Theresa. "This is the declaration of Justin's innocence. I'm confident General Mattis will do what is right."

By clearing Sharratt in the shootings of Jasib Aiad Ahmed, Kahtan Aiad Ahmed and Jamal Aiad Ahmed, Ware also appeared to clear Wuterich in that attack, concluding that the Marines' account was more credible than the allegations of residents who said the deaths were executions. Ware found that physical evidence showed that the shots that killed the men were fired from a distance, "inconsistent with an execution."

Wuterich is also charged in other slayings that day. However, Ware did not examine the previous shootings, reporting that it is only a "compelling theory tying in the events and actions by other Marines as a prelude for the actions" Sharratt took later that day.

Civilians interviewed by the Naval Criminal Investigative Service said that the Marines came to the final house and separated women and children before leading the men back inside to kill them. Ware found their accounts questionable and inconsistent.

"To believe the government version of facts is to disregard clear and convincing evidence to the contrary and sets a dangerous precedent that . . . may encourage others to bear false witness against Marines as a tactic to erode public support of the Marine Corps and mission in Iraq," Ware wrote.

Gary Myers and James Culp, civilian attorneys for Sharratt, said in a joint statement that they are pleased with the report and that earlier "prejudgment within some elements of the media and by certain members of Congress was particularly offensive to us," a thinly veiled reference to comments by Rep. John P. Murtha (D-Pa.) last year that the shootings were cold-blooded murders.

If his charges are dropped, Sharratt would be the second enlisted Marine to be cleared in the case. Cpl. Sanick Dela Cruz, who admitted shooting the men near the car, had his charges dropped and was granted immunity. Wuterich and Lance Cpl. Stephen Tatum are charged with murder and are scheduled for Article 32 hearings.